Friday, June 25, 2010

Memo to Apple: Humans conduct electricity

Perhaps you saw the news stories reporting many complaints about signal loss on the new Apple iPhone 4? (Here is one from yesterday.)

As I guessed, the problem is not with the antenna itself, but the fact that there are two antennas on the phone, separated by a small distance on the case. (See this news story, among others, on what the user must not do and how to fix it.)

The problem is that humans conduct electricity. No problem if there is only one antenna, since that just makes you part of the antenna if you touch it. The problem arises when the user short circuits the gap between the two antennas by touching both sides at the same time. (That means a quick fix would be a bit of electrical tape around that corner until you get the more expensive, but better looking, plastic or rubber case mentioned in the articles.) And since MSNBC does not have a physicist in the news room ... I'll add that connecting the cell and network antennas certainly could explain the problem.

It changes the tuning of both antennas, which is bad enough, but it also means that one poor antenna is feeding two separate receiver circuits rather than each one getting its own signal. It would also short the transmitted signal from one side into the input for the other side, reducing the energy that goes out of the antenna to the cell tower. I have no clue at all what those circuits look like, but a decent impedance match could kill the outgoing signal needed to keep the "line" to the cell tower open.

I don't have one or I would do the simple experiment of shorting the gap with a potentiometer to watch what happens as the gap resistance varies.

1 comment:

Unbalanced Reaction said...

I think there is a new freshman physics lab exercise in this post!!